The map to the left shows the counties which voted for Obama (blue) and McCain (red) in the 2008 election. The blue counties are part of the Black Belt, the area where blacks are a majority of the population because of the economic concentration of cotton culture during the 19th and 20th centuries. The McCain Belt, those counties where John McCain beat George W. Bush, is getting some press, but obviously it is interesting to wonder about areas where large black populations which increased turnout are likely masking the shift of the white vote for John McCain. I have already shown on a state-by-state basis where the white vote shifted toward the Democrats in 2008, and where it shifted toward the Republicans. Though the average white vote budged only a bit, there is important regional structure which is being masked by aggregating all this information.
The political scientist Larry Bartels reaffirms my basic point:
However, there is a good deal of circumstantial evidence suggesting that racial resentment eroded Obama's support among white voters. His gains relative to Kerry were significantly smaller in states with large numbers of African-Americans--a pattern disguised in the overall vote totals by his strong support among African-Americans themselves. In the former Confederacy he gained only slightly over Kerry among white voters, despite making big gains in two key swing states, North Carolina and Virginia. The only states in the country in which he lost more than a point or two of white support were Louisiana, Alabama, Arkansas, and Mississippi.
You can see this in the exit polls. They rather straightforwardly illustrate that Obama won a smaller percentage of the white vote than Kerry in many states in the South. But I decided to look at it a different way: I plotted the percentage of whites in each county and their vote percentages for Barack Obama and John Kerry in Mississippi. This is more precise than an exit poll because votes are votes, and the Census counts everyone. So here is that chart:
As you can see, as the percentage of whites increases the proportion voting for the Democrat decreases. This is no surprise. In this part of the South the Republicans are the white party, and the Democrats are the black party. But look at the slopes: it is higher in 2008 than 2004. That means that the white vote for Obama was lower and the black vote for him higher. The "ends" of the line swiveled so that the slope tilted up. If I assume that this is modeled by a linear regression, the r-squared for 2008 is 0.93 and for 2004 it is 0.76. If I assume that this is a logistic curve the r-squared for 2008 is 0.90 and for 2004 is 0.81. The r-squared can be interpreted so that one can say that ~90% of the variation on a state wide level in voting for Democrats could be explained by the proportion who were white in the counties in 2008. In 2004 the equivalent value would be ~75-80%. Both of these values are high, but, it suggests that the exit polls are right, and racial polarization has increased over the 4 years. Whiteness is a nearly perfect proxy for the Republican presidential vote now, and blackness the Democratic vote. And these associations have increased between 2004 and 2008.
But it isn't as if Mississippi is one homogeneous state with one culture. Among whites there are those who are basically in Appalachia, while others who live in the lowland South. So I decided to constrain the chart to counties with various intervals of the white %. Here is a chart of only the majority black counties:
Here are majority white counties:
And here are counties where 62% or more are white, which is the proportion in Mississippi which is white (so these are the whiter counties in the state):
It looks to me that what you're seeing are two things:
1) Increased black turnout in counties where many blacks weren't voting. I think the black turnout went up nationally by about 10% (that is, from 11% to 12% of the electorate), but there might be regional disparities in terms of where that 10% is coming from.
2) Some white people in mostly white counties switched from Democrats to Republicans.
I assume in majority black counties you're pretty much as polarized as you can get; very few white Democrats and black Republicans. In the overwhelmingly white counties there's less polarization because the fact that there are few black people means that white Democrats aren't a member of the black party, at least locally. But it looks like the emergence of Obama changed things even in very white counties, where there is a discernible drop off in white support, with obviously far less compensation from the relatively small black minority turning out a higher rate. If you're wondering about what that one outlier on the chart which is far away from the trendlines, it's Alcorn county in Mississippi's far north. It's not a data entry error, that was my first thought....
Here's the raw data:
Razib, I don't know if you follow the Horserace blog (http://www.realclearpolitics.com/horseraceblog), but Jay Cost examined very similar questions vis-a-vis Obama vs. Hillary this spring. The question was a bit different -- what is Obama's voting coalition, and how does Hillary break into it, but there were regional differences that appeared at that point and that still appear in the Obama/McCain match-up. The series is worth reading if you haven't.